cannot instantiate abstract class

I have a c++ applicaiton (as below) and I'm getting a linker error
that has me stumped. error C2259: 'myspace::PolicyImpl<T>': cannot
instantiate abstrace class.

If it's obvious to anybody what I'm doing wrong, please let me know.

Thanks,
PaulH

// MyClass.h
namespace myspace {
    template< typename T, template< typename > class ClassPolicy =
Policy >
    class ClassA
    {
    public:
        virtual void Update( const T& hint ) = 0;
    };

    template < typename T >
    class Policy
    {
    public:
        virtual void RemoveAll( ClassA< T, myspace::Policy > *p ) = 0;
        virtual void Add( ClassB< T, myspace::Policy > *p ) = 0;
        virtual void Remove( ClassB< T, myspace::Policy > *p ) = 0;
    };
}

// MyClassImpl.h
namespace myspace {
    template< typename T, template< typename > class ClassPolicy =
PolicyImpl >
    class ClassAImpl : public ClassA< T, ClassPolicy >
    {
    public:
        virtual ~ClassAImpl()
        {
            //...
        }
        void Update( const T& hint )
        {
            //...
        }
    private:
        ClassPolicy< T > classpolicy_; // ***linker ERROR C2259
here***
    };

    template < typename T >
    class PolicyImpl : public Policy< T >
    {
    public:
        PolicyImpl(){};
        void RemoveAll( ClassA< T, myspace::PolicyImpl > *p )
        {
            //...
        }
        void Add( ClassB< T, myspace::PolicyImpl > *p )
        {
            //...
        }
        void Remove( ClassB< T, myspace::PolicyImpl > *p )
        {
            //...
        }
    private:
        //...
    };
}

The full text of the error message is:
1>MyClassImpl.h(45) : error C2259: 'myspace::PolicyImpl<T>' : cannot
instantiate abstract class
1> with
1> [
1> T=ClientConnectMsg
1> ]
1> due to following members:
1> 'void
myspace::Policy<T>::RemoveAll(myspace::ClassA<T,ClassPolicy> *)' : is
abstract
1> with
1> [
1> T=ClientConnectMsg,
1> ClassPolicy=myspace::Policy
1> ]
1> ClassA.h(43) : see declaration of
'myspace::Policy<T>::RemoveAll'
1> with
1> [
1> T=ClientConnectMsg
1> ]
1> MyClassImpl.h(60) : see reference to class template
instantiation 'myspace::ClassAImpl<T,ClassPolicy>' being compiled
1> with
1> [
1> T=ClientConnectMsg,
1> ClassPolicy=myspace::PolicyImpl
1> ]
1> MyClassImpl.h(57) : while compiling class template member
function 'myspace::ClassBImpl<T>::~ClassBImpl(void)'
1> with
1> [
1> T=ClientConnectMsg
1> ]
1> UsingClass.h(61) : see reference to class template
instantiation 'myspace::ClassBImpl<T>' being compiled
1> with
1> [
1> T=ClientConnectMsg
1> ]